A refractive error is a problem in the light focusing abilities of the eye and is one of the foremost reasons for reduced visual clarity.
Types of Refractive Errors:
- Spherical Errors
- Cylindrical Errors
- Presbiopia
- Anisometropia
Spherical Errors: They occur when the focusing power of the eyes is too strong or too weak to focus light onto the retina. This can again be of 2 types, namely
Myopia: When the focusing power is too large compared to the size of the eyeball. In other words, distant objects appear blurred while objects closer to the eye appear clearly.
Hyperopia: When the focusing power is too weak compared to the eyeball. As a result both the distant and near objects appear blurred, with more blurriness to nearer objects.
Cylindrical Errors: This condition is also called Astigmatism. It occurs when the focusing power of the eye is too strong or too weak across the field of vision. Also, the lens tend to behave like a cylindrical lens along the field of vision.
Presbiopia: Here, the eye loses the power of dynamic accommodation. This means that the eye cannot adjust its focus for viewing objects at various distances. It simply loses its flexibility.
Anisometropia: In this condition, both the eyes show refractive errors, but their strengths (power of focus) are different.
Causes of Refractive Errors:
Though refractive errors can occur for various reasons, the most frequent causes are:
- Genetic factors
- Environmental factors
- Combination of both
- Trauma due to accidents or other diseases
- Ocular disorders occurring by birth.
- Other reasons such as excessive staring, frowning and excessive blinking and rubbing of eyes could result in refractive errors, especially in children.
Signs of Refractive Errors:
The main symptom or sign of these errors is fussy appearance of objects at certain distances; distant, near or both.
Diagnosis
Regular visits to the ophthalmologist or an optometrist will help screen these conditions at the earliest.
Treatment
- Myopia, can be corrected using a concave (minus) lens.
- Hyperopia, can be corrected using a convex (plus) lens.
- Astigmatism can be corrected using a cylindrical lens (a segment or portion cut from a cylinder).
- Presbiopia can be corrected using a convex (plus) lens to help view near objects, along with a concave lens for distant objects. These may be supplied as separate spectacles or built into one single lens. They are called as bifocal lenses and variable focus lenses.
- Anisometropia can be corrected only with the use of contact lenses as normal glasses cause perception problems.
